In situ combustion offers one approach for recovering oil from reservoirs in certain geologic formations. With in situ combustion, an oxidant injected through an injection well into the reservoir reacts with some of the oil to propagate a combustion front through the reservoir. This process heats the oil ahead of the combustion front. Further, the injection gas and combustion gasses drive the oil that is heated toward an adjacent production well.
Success of the in situ combustion in a heavy oil or bitumen environment depends on stability of the combustion front and ability to ensure that oxidation occurring is an exothermic reaction. Amount of beneficial thermal cracking of the oil to make the oil lighter tends to increase with higher temperatures from the oxidation. Further, oxidation of the oil by an endothermic reaction can create hydrogen bonding and result in undesired increases in viscosity of the oil.
Various factors attributed to failure of the in situ combustion include loss of ignition, lack of control, and inadequate reservoir characterization. For maximum recovery of the oil, the combustion front must be able to stay ignited in order to sweep across the entire reservoir. Due to issues such as formation heterogeneity influencing the combustion front, prior approaches often result in instability of the combustion front, premature extinguishing of the combustion front, or inability to achieve or maintain desired temperatures.
Therefore, a need exists for improved methods and systems for oil recovery with in situ combustion.